Cs4 PbBr6 Research Articles

Self-Assembly of Perovskite Crystals Anchored Al2 O3 -La2 O3 Nanofibrous Membranes with Robust Flexibility and Luminescence.

Inorganic luminescent materials as one of the important high-performance materials are widely used for industry and scientific research, mainly owing to their outstanding luminescence properties. However, inorganic luminescent materials are typically brittle and inelastic, which greatly limit their use in practical applications, particularly in flexible optoelectronic devices. In this work, it is shown that "plum-pudding" like CsPbBr3 /Cs4 PbBr6 perovskite crystals anchor onto Al2 O3 -La2 O3 (CCAL) nanofibrous membranes, which are synthesized via a facile electrospinning and subsequent supersaturated recrystallization process. The as-synthesized CCAL membranes exhibit outstanding mechanical flexibility and luminescence properties. Meanwhile, the crystal structure and luminous performance of the CCAL membranes are regulated by different molar ratios of CsBr/PbBr2 . The photoluminescence reaches a maximum value for the CCAL membranes produced with a CsBr/PbBr2 ratio of 1, and shows a narrow emission line-width of 18 nm. Furthermore, the potential applications of the CCAL nanofibrous membranes in green light devices through a remote nanofibrous membranes packaging approach are demonstrated. A pure green emission is achieved with the Commission Internationale de L'Eclairage color coordinates of (0.28, 0.65). This facile strategy would open a new avenue to flexible inorganic luminescent materials for the lighting and backlight display industries.

High-Purity Inorganic Perovskite Films for Solar Cells with 9.72 % Efficiency.

All-inorganic perovskite solar cells with high efficiency and improved stability are promising for commercialization. A multistep solution-processing method was developed to fabricate high-purity inorganic CsPbBr3 perovskite films for use in efficient solar cells. By tuning the number of deposition cycles (n) of a CsBr solution, the phase conversion from CsPb2 Br5 (n ≤3), to CsPbBr3 (n=4), and Cs4 PbBr6 (n≥5) was optimized to achieve vertical- and monolayer-aligned grains. Upon interfacial modification with graphene quantum dots, the all-inorganic perovskite solar cell (without a hole-transporting layer) achieved a power conversion efficiency (PCE) as high as 9.72 % under standard solar illumination conditions. Under challenging conditions, such as 90 % relative humidity (RH) at 25 °C or 80 °C at zero humidity, the optimized device retained 87 % PCE over 130 days or 95 % over 40 days, compared to the initial efficiency.

All-Solid-State Mechanochemical Synthesis and Post-Synthetic Transformation of Inorganic Perovskite-type Halides.

All-inorganic and hybrid perovskite type halides are generally synthesized by solution-based methods, with the help of long chain organic capping ligands, complex organometallic precursors, and high boiling organic solvents. Herein, a room temperature, solvent-free, general, and scalable all-solid-state mechanochemical synthesis is demonstrated for different inorganic perovskite type halides, with versatile structural connectivity in three (3D), two (2D), and zero (0D) dimensions. 3D CsPbBr3 , 2D CsPb2 Br5 , 0D Cs4 PbBr6 , 3D CsPbCl3 , 2D CsPb2 Cl5 , 0D Cs4 PbCl6 , 3D CsPbI3 , and 3D RbPbI3 have all been synthesized by this method. The all-solid-state synthesis is materialized through an inorganic retrosynthetic approach, which directs the decision on the solid-state precursors (e.g., CsX and PbX2 (X=Cl/Br/I) with desired stoichiometric ratios. Moreover, post-synthetic structural transformations from 3D to 2D and 0D perovskite halides were performed by the same mechanochemical synthetic approach at room temperature.

Superior Self-Powered Room-Temperature Chemical Sensing with Light-Activated Inorganic Halides Perovskites.

Hybrid halide perovskite is one of the promising light absorber and is intensively investigated for many optoelectronic applications. Here, the first prototype of a self-powered inorganic halides perovskite for chemical gas sensing at room temperature under visible-light irradiation is presented. These devices consist of porous network of CsPbBr3 (CPB) and can generate an open-circuit voltage of 0.87 V under visible-light irradiation, which can be used to detect various concentrations of O2 and parts per million concentrations of medically relevant volatile organic compounds such as acetone and ethanol with very quick response and recovery time. It is observed that O2 gas can passivate the surface trap sites in CPB and the ambipolar charge transport in the perovskite layer results in a distinct sensing mechanism compared with established semiconductors with symmetric electrical response to both oxidizing and reducing gases. The platform of CPB-based gas sensor provides new insights for the emerging area of wearable sensors for personalized and preventive medicine.

Dual-Phase CsPbBr3 -CsPb2 Br5 Perovskite Thin Films via Vapor Deposition for High-Performance Rigid and Flexible Photodetectors.

Inorganic perovskites with special semiconducting properties and structures have attracted great attention and are regarded as next generation candidates for optoelectronic devices. Herein, using a physical vapor deposition process with a controlled excess of PbBr2 , dual-phase all-inorganic perovskite composite CsPbBr3 -CsPb2 Br5 thin films are prepared as light-harvesting layers and incorporated in a photodetector (PD). The PD has a high responsivity and detectivity of 0.375 A W-1 and 1011 Jones, respectively, and a fast response time (from 10% to 90% of the maximum photocurrent) of ≈280 µs/640 µs. The device also shows an excellent stability in air for more than 65 d without encapsulation. Tetragonal CsPb2 Br5 provides satisfactory passivation to reduce the recombination of the charge carriers, and with its lower free energy, it enhances the stability of the inorganic perovskite devices. Remarkably, the same inorganic perovskite photodetector is also highly flexible and exhibits an exceptional bending performance (>1000 cycles). These results highlight the great potential of dual-phase inorganic perovskite films in the development of optoelectronic devices, especially for flexible device applications.

Imbedded Nanocrystals of CsPbBr3 in Cs4 PbBr6 : Kinetics, Enhanced Oscillator Strength, and Application in Light-Emitting Diodes.

Solution-grown films of CsPbBr3 nanocrystals imbedded in Cs4 PbBr6 are incorporated as the recombination layer in light-emitting diode (LED) structures. The kinetics at high carrier density of pure (extended) CsPbBr3 and the nanoinclusion composite are measured and analyzed, indicating second-order kinetics in extended and mainly first-order kinetics in the confined CsPbBr3 , respectively. Analysis of absorption strength of this all-perovskite, all-inorganic imbedded nanocrystal composite relative to pure CsPbBr3 indicates enhanced oscillator strength consistent with earlier published attribution of the sub-nanosecond exciton radiative lifetime in nanoprecipitates of CsPbBr3 in melt-grown CsBr host crystals and CsPbBr3 evaporated films.

CsPb2 Br5 Single Crystals: Synthesis and Characterization.

CsPb2 Br5 is a ternary halogen-plumbate material with close characteristics to the well-reported halide perovskites. Owing to its unconventional two-dimensional structure, CsPb2 Br5 is being looked at broadly for potential applications in optoelectronics. CsPb2 Br5 investigations are currently limited to nanostructures and powder forms of the material, which present unclear and conflicting optical properties. In this study, we present the synthesis and characterization of CsPb2 Br5 bulk single crystals, which enabled us to finally clarify the material's optical features. Our CsPb2 Br5 crystal has a two-dimensional structure with Pb2 Br5- layers spaced by Cs+ cations, and exhibits approximately 3.1 eV indirect band gap with no emission in the visible spectrum.

Solution‐Grown CsPbBr3/Cs4PbBr6 Perovskite Nanocomposites: Toward Temperature‐Insensitive Optical Gain

With regards to developing miniaturized coherent light sources, the temperature-insensitivity in gain spectrum and threshold is highly desirable. Quantum dots (QDs) are predicted to possess a temperature-insensitive threshold by virtue of the separated electronic states; however, it is never observed in colloidal QDs due to the poor thermal stability. Besides, for the classical II-VI QDs, the gain profile generally redshifts with increasing temperature, plaguing the device chromaticity. Herein, this paper addresses the above two issues simultaneously by embedding ligands-free CsPbBr3 nanocrystals in a wider band gap Cs4 PbBr6 matrix by solution-phase synthesis. The unique electronic structures of CsPbBr3 nanocrystals enable temperature-insensitive gain spectrum while the lack of ligands and protection from Cs4 PbBr6 matrix ensure the thermal stability and high temperature operation. Specifically, a color drift-free stimulated emission irrespective of temperature change (20-150 °C) upon two-photon pumping is presented and the characteristic temperature is determined to be as high as ≈260 K. The superior gain properties of the CsPbBr3 /Cs4 PbBr6 perovskite nanocomposites are directly validated by a vertical cavity surface emitting laser operating at temperature as high as 100 °C. The results shed light on manipulating optical gain from the advantageous CsPbBr3 nanocrystals and represent a significant step toward the temperature-insensitive frequency-upconverted lasers.

Highly Emissive Green Perovskite Nanocrystals in a Solid State Crystalline Matrix.

Perovskite nanocrystals (NCs) have attracted attention due to their high photoluminescence quantum yield (PLQY) in solution; however, maintaining high emission efficiency in the solid state remains a challenge. This study presents a solution-phase synthesis of efficient green-emitting perovskite NCs (CsPbBr3 ) embedded in robust and air-stable rhombic prism hexabromide (Cs4 PbBr6 ) microcrystals, reaching a PLQY of 90%. Theoretical modeling and experimental characterization suggest that lattice matching between the NCs and the matrix contribute to improved passivation, while spatial confinement enhances the radiative rate of the NCs. In addition, dispersing the NCs in a matrix prevents agglomeration, which explains their high PLQY.

Multiple Charge Transfer Dynamics in Colloidal CsPbBr3 Perovskite Quantum Dots Sensitized Molecular Adsorbate

Ultrafast charge-transfer (CT) dynamics has been verified in CsPbBr3 (CPB) quantum dot (QD)–4,5-dibromofluorescein (DBF) composite materials, which form a strong CT complex in the ground state and can absorb more photons in the red region of the solar spectrum. Cyclic voltammetry and steady state luminescence studies suggest that the conduction (CB) and valence bands (VB) of CPB lie, respectively, below the LUMO and the HOMO of the DBF molecule. Steady state and time-resolved luminescence measurements with selective photoexcitation reveal the photoexcited hole transfer from CPB QDs to the DBF molecule, which is thermodynamically viable. Additionally, a red-shifted PL band was detected upon excitation of the CT complex that has been attributed to CT luminescence. Femtosecond transient absorption measurements have been performed to measure the hole transfer and direct electron transfer processes in the composite system and have been measured to be 1–1.25 ps and <100 fs, respectively. Dual behavior of the DB...

Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb2 Br5 Nanoplatelets and Their Fast Anion Exchange.

All-inorganic cesium lead-halide perovskite nanocrystals have emerged as attractive optoelectronic nanomaterials owing to their stabilities and highly efficient photoluminescence. Herein we report a new type of highly luminescent perovskite-related CsPb2 Br5 nanoplatelets synthesized by a facile precipitation reaction. The layered crystal structure of CsPb2 Br5 promoted an anisotropic two-dimensional (2D) crystal growth during the precipitation process, thus enabling the large-scale synthesis of CsPb2 Br5 nanoplatelets. Fast anion exchange has also been demonstrated in as-synthesized CsPb2 Br5 nanoplatelets to extend their photoluminescence spectra to the entire visible spectral region. The large-scale synthesis and optical tunability of CsPb2 Br5 nanoplatelets will be advantageous in future applications of optoelectronic devices.